Question

A compound(C₁₀H₁₂0₂)whose spectrum is shown here was isolated from a reaction mixture containing 2-phenylethanol and acetic acid.

1. Propose a structure for this compound.
2. Assign peaks to show which protons give rise to which signals in the spectrum.

Short answer

a)

Phenethyl acetate

b)

a = δ 7.2-7.3 (multiplet, 5H) , b = δ 4.3 (triplet, 2H) , c = δ 2.9 (triplet, 2H) ,

d = δ 2.0 (singlet, 3H)

Step-by-step solution

Explanation of part (a):

A compound having molecular formula (C₁₀H₁₂0₂), must have been formed through the reaction of 2-phenylethanol and acetic acid. Alcohol and acid combine to form ester as the product. The reaction is known as esterification reaction and usually takes place in presence of acid catalyst.

Formation of Phenethyl acetate

Explanation of part (b):

The chemical shift values depend on the nearby environment and the electronegativities of neighbouring atoms also. If a neighboring atom is more electronegative, then the chemical shift value of a proton which is near to that electronegative atom or adjacent to it will be higher and it will be in a deshielded environment. Benzene protons have a chemical shift value of around 7.2-7.3. Proton-b, which is adjacent to the oxygen atom, will have a high value of chemical shift, that is, 4.3. Proton-d will have a chemical shift value of 2.0 due to shielded environment.

The chemical shift values of protons in phenethyl acetate will be,

a = δ 7.2-7.3 (multiplet, 5H) , b = δ 4.3 (triplet, 2H) , c = δ 2.9 (triplet, 2H) ,

d = δ 2.0 (singlet, 3H)

Different kinds of protons have different chemical shifts in phenethyl acetate